The present invention relates generally to spring seals, and more particularly, to a fluid pressure activated piston return spring seal that may be employed in a disk brake braking system to achieve increased piston bore stroke.
In disk brake braking systems, pressure is typically applied to a piston by way of a braking fluid and the piston moves a brake lining into contact with a brake disk to retard rotational movement. As should be understood, it is necessary to provide a biasing device to return the piston and the brake lining from the pressurized braking position to a relaxed position. As can be seen from U.S. Pat. Nos. 4,229,013 and 4,342,463, hereby incorporated by reference, it is known to provide a spring seal assembly having a seal element which (1) seals the braking fluid, (2) grips the piston and becomes deflected when the piston and spring seal assembly are pressurized by the fluid and move to provide braking action, and (3) provides a biasing force to retract the piston and move the piston to its initial position when the fluid pressure is removed. Accordingly, the piston and the associated lining are withdrawn a sufficient distance to prevent the lining from remaining in contact with the brake disk and to allow free rotational movement of the brake disk.
However, a spring seal assembly as described in the aforementioned references has a serious disadvantage in that the deflection of the seal element and the resultant stroke of the piston are limited. More specifically, since the seal element in toroidal cross-section has a generally planar pressure side or face, the maximum deflection of the seal element and the resultant maximum bore stroke of the piston is approximately 10 percent of the seal cross-section, a value too small to meet brake system performance requirements under some circumstances.
In an effort to increase the seal element deflection and piston stroke of the aforementioned spring seal assembly, the dimensions of the seal element in toroidal cross-section were proportionally increased. However, the increased size seal element required increased fluid pressure for full piston deflection operation and otherwise did not provide adequate increased deflection and piston stroke.
A need exists, then, for a spring seal assembly having a seal element with increased deflection and providing increased piston stroke while still maintaining a reliable seal. More particularly, a need exists for a spring seal assembly having a seal element with a toroidal cross-sectional shape that allows a pressurized piston to deflect a relatively large distance of about 0.120 inches or more from an un-pressurized initial position and that provides sufficient biasing force to return the piston to the initial position when the pressure is removed.